Tunable filters may be used for many different applications, such as tunable lasers, tunable add-drop multiplexers, tunable dispersion compensation, and tunable receivers. Where the filters are used in a tunable laser, for example, the filters select one of several wavelengths used by the laser. One implementation for a tunable laser monolithically integrates the tunable filter with thermal resistance and a mechanically stiff mounting, using a tensile-strained thin-film thermal resistor fashioned from silicon nitride. This implementation requires a relatively inefficient use of wafer area to accommodate the thermal resistance function. Further, the placing of the various fabrication steps in series results in yield and latency hits.
Another tunable laser uses a micro-hotplate as a sub-mount, but a sub-mount without structuring. A simple diced glass plate does not provide a sufficiently high thermal resistance for a given size so as to permit low power operation of the thin bulk etalon temperature tunable filters (˜150 microns Si) for standard telecom form factors and tuning ranges.
Thus, there is a continuing need for a structured sub-mount for a tunable filter that overcomes the shortcomings of the prior art.